The present invention relates to an internal mounting panel for an automobile for covering an air bag device, and its manufacturing method.
When the automobile receives an impact, the air bag device senses its impact, and expands and develops an air bag and interposes the air bag between an automobile body and a crew member so that the air bag device protects the crew member.
The air bag device is rapidly spread in recent years, and its arranging place is not only a steering wheel for the driver's seat and an instrument panel for the passengers's seat, but the air bag for a side portion for protecting the occupant from the impact of the side face portion is also arranged in the upper portion of an automobile body side window.
For example, in the air bag device for the passenger's seat arranged within the instrument panel, an air bag cover body as the internal mounting panel for covering this air bag device is prepared as a separate object different from the instrument panel. This air bag cover body is usually assembled into an opening portion arranged in the instrument panel. However, in recent years, these members are integrated and formed as a module so that manufacturing and assembly works are rationalized. Further, it is required to improve the external appearance of the instrument panel as an internal mounting part by removing a joint.
Thus, a member obtained by integrating the air bag cover body with the instrument panel is already proposed. For example, the member described in JP-A-11-291069 is known. In this laid-open patent, the instrument panel having no opening portion for the air bag is injection-molded, and laser processing is performed in a portion corresponding to an air bag storing position on this panel rear face so that a breaking prearranging line is formed.
However, in this method for post-processing the breaking prearranging line, a laser processor for this processing is required and a slight processing work is required after the molding, etc. Accordingly, there are problems in view of cost and productivity.
Further, the molding method for forming the breaking prearranging line for developing the air bag cover body in the molding process which requires no post-processing is also proposed in JP-A-2002-234413.
Another molding method is also proposed in JP-A-2003-146171. In this method, when the breaking prearranging line is processed in a hard in-panel constructed by a hard material at the molding time, a block having needle-shaped pins is advanced and retreated within a cavity in this processing. Further, the appearance of the breaking prearranging line on the surface of a block pressing trace is prevented by raising the temperature of a die surface of the opposite side than the block temperature of a breaking prearranging line processing face.
This method is a rational method since no post-processing is required. However, it is necessary to arrange a core and the block for forming the breaking prearranging line within the molding die so as to be freely advanced and retreated. Further, the die becomes complicated and the molding method also becomes complex.
Further, since the instrument panel is an internal mounting part, its external appearance and feel are also important. Therefore, there have been proposed various types of two-layer structure in which a surface layer of this panel is constructed by a soft material having a soft feeling, which is laminated on a base material layer.
However, when such a two-layer structure is set, it is technically difficult to stably obtain predetermined breaking characteristics. Namely, the present inventors have known that a technical means for stably generating the breaking of a skin layer toward just above a groove portion arranged in the base material layer is required from various trial results based on teaching of the above prior art.
It is presumed that this is because the air bag cover is not necessarily uniformly pushed up from the downward air bag, and the breaking is easily caused in the direction inclined with respect to the just above direction by applying shearing force due to uneven rising. For example, in the cover of a single flap type (open side type), there is a relation in which the air bag cover is un-uniformly pushed up in the relation of a door forming portion and its peripheral edge. In the cover of a twin flap type (double hinged type), there is a relation in which the air bag cover is further un-uniformly pushed up in the relation of flaps adjacent to each other. This breaking angle can be set to a direction similar to the just above direction in a certain place, and is inclined in a certain case. The inclination angle at that time does not easily become constant. Therefore, the selection of a material for obtaining predetermined desirable breaking characteristics, the specification of a molding processing condition to stably utilize physical properties of this specified material, and strict quality management are required. Therefore, there is a fear that cost is greatly increased.
In the air bag cover of such a structure of plural layers, there is also a proposal for reliably breaking the breaking prearranging line by smaller force. In JP-T-2000-512953, the construction of a two-layer air bag cover body is proposed. In this construction, the two-layer air bag cover body is constructed such that the cover body can be broken by smaller force without continuously breaking the cover body over the end portion of an intended breaking line, and opening force and breaking force are changed without changing visual and/or mechanical characteristics in the cover body of the air bag having a cover layer of a smooth surface.
In accordance with such a construction, the breaking line is formed at the edge between portions in which the surface layer and the base material layer are extended into their mutual layers in the groove portion of the base material layer.
In accordance with such a construction, the breaking is caused on the contact face of two layers adjacent to each other. Accordingly, it is considered that the breaking can be more reliably generated as designed along the breaking prearranging line.
There is an internal mounting part having a skin arranged through foaming polyurethane in the base material layer of polypropylene as a technique of the internal mounting part not considering formation of an air bag deployment door. However, since an adhering property is inferior in polypropylene and polyurethane, the internal mounting part is manufactured by a method for molding the polyurethane surface layer by insert molding after the base material layer surface of polypropylene is coated with a primer.
This molding method is inferior in working property and also has disadvantage in cost since the primer is used.
There is also another proposal with respect to this problem. For example, JP-A-9-11246 discloses a method in which preprocessing for forming an irregular coarse face by a water jet with respect to the surface of the polypropylene base material layer is performed instead of the primer processing, and the polypropylene base material layer is then arranged in a die and the polyurethane molding material is filled between the die and the skin and is foamed and molded. In accordance with this method, adhesive force is improved by an anchor effect using the coarse face formation processing.
However, the internal mounting panel able to be adapted for the development of the air bag must be reliably broken at a breaking prearranging position during the operating time of the air bag device, and the air bag must be smoothly developed. In the construction of the normal instrument panel in which there is no breaking prearranging portion in the skin and the polyurethane layer as in the above method, it is difficult to set the internal mounting panel reliably broken in the predetermined position even when this instrument panel is applied to the air bag cover as it is. Therefore, it is necessary to take a structural countermeasure to reliably cause the breaking in the predetermined position. Namely, a weak portion is formed in the base material layer after the molding. Further, in a position corresponding to this weak portion, a weak portion is also formed in the surface layer constructed by the polyurethane layer and the skin. Therefore, processes are further added so that productivity is reduced.
Further, it is technically difficult to stably obtain predetermined breaking characteristics even when a two-layer structure of the polyurethane surface layer and the base material layer including no skin is set.
No layer separation using impact force at the above internal mounting panel breaking time can be sufficiently avoided by adhesive force using the coating of the conventional primer and the coarse face formation processing using the water jet. Therefore, no stable opening-tearing behavior at the air bag developing time can be obtained.
JP-A-2000-16216 proposes various structures in which the surface layer of this panel is constructed by a soft material having a soft feeling and is laminated on the base material layer. Further, in another proposed method, this surface layer is set to a skin constructed by a skin layer, a foaming layer and a barrier layer and is inserted and the base material layer is insert-molded.
This breaking prearranging portion is constructed by a cut-removing portion extended from the surface side of the base material layer to the barrier layer of the skin, and a small hole able to break the skin layer is formed in a corresponding portion of the skin layer.
As mentioned above, the internal mounting panel as the air bag cover body is an internal mounting part of the automobile, and its external appearance and feel are also important.
When a contact face for mutually extending the above surface layer and the base material layer is set to the breaking line, a thin wall portion is also formed on the surface layer side. However, as a result, since the thin wall portion is further arranged in the surface layer originally having a small thickness, it also has a visual influence on the surface side of this thin wall portion and the breaking prearranging line is visually recognized. Further, when a vehicle occupant comes in contact with the contact face with a hand and fingers, its touch is different from the circumferential touch. Therefore, a problem is caused in the outward appearance and the feel.
Further, since the thin wall portion is further arranged in the surface layer having a soft feeling and set to be originally thin on the base material layer having a groove, the thin wall portion is easily broken at the operating time of the air bag. On the other hand, there is also a fear that this thin wall portion is mechanically weak and can be damaged at the normal time.
Further, at the operating time of the air bag device, the internal mounting panel must be reliably broken in the breaking prearranging position, and the air bag must be smoothly developed. In the construction of the normal instrument panel in which there is no breaking prearranging portion in the skin and the polyurethane layer as in the above method, it is difficult to set the internal mounting panel reliably broken in the predetermined position even when this construction is applied to the internal mounting panel as it is. Therefore, it is necessary to take a structural countermeasure to reliably break the internal mounting panel in the predetermined position. Namely, it is necessary to form the weak portion in the base material layer after the molding, and also form another weak portion in the surface layer constructed by the polyurethane layer and the skin in the position corresponding to this weak portion. Therefore, processes are further added and productivity is reduced.
Further, it is technically difficult to stably obtain predetermined breaking characteristics even when the two-layer structure of the polyurethane surface layer and the base material layer including no skin is set.
In the air bag cover having the skin having a cushion layer, small hole processing is also required as mentioned above on the skin side in a breaking prearranging portion corresponding position after the skin molding so as to smooth this breaking. Therefore, there is a problem in productivity. Further, although it is the small hole, there is a problem in the external appearance since the hole exists in the skin.